A conventional disk drive usually contains a single disk media for data storage. For example, a conventional hard disk drive contains only magnetic disk media, and a solid state drive (SSD) contains only flash media. Recently, hybrid storage devices, which combine different storage media in a single device, have drawn increasing interests from storage vendors and customers. Hybrid storage devices could be in many different forms. Just to name a few, a hybrid disk drive may contain a conventional disk media plus a non-volatile memory (NVM), in which the NVM serves as a data cache to the disk media for performance and energy efficiency purposes; an SSD may contain large capacity and low cost multi-level cells as well as small capacity and high cost and performance phase change memory. Besides single hybrid storage devices, a hybrid storage array is often seen in the market. A hybrid disk array may be an array of conventional hard disk drives (HDDs) with an extra NVM or SSD cache device attached to the array controller. The array may instead include SSDs and large amount of HDDs. The objective of having hybrid storage device/array may include achieving high capacity and high performance and/or low power consumption with low cost.
Certain storage media/recording technology may require special way to access it. For example, NAND flash can only be written sequentially within a data block. Similarly, shingled magnetic recording (SMR) disks may only be written through appending and not updating-in-place.